Some claim that standard Arabic has been intentionally made more complicated because writers were paid well by rulers back in old days, and there were more incentives to make grammar hard for the ordinary folks, so that you need "craftsmen" to write according to an Arabic linguist.Until the 80s in many Arab countries you needed clerks to produce documents from governments. (Comedy sketch on it https://www.youtube.com/watch?v=wtloJgMgFho) Arabic linguist https://www.youtube.com/watch?v=UoqDR0Hd9f0
'Category V – It usually takes 88 weeks or 2200 hours to reach S-3/R-3 proficiency in these languages. This small group of “super-hard languages” includes Chinese (Mandarin), Cantonese, Japanese, Korean and Arabic.' (Arabic linguist)https://www.youtube.com/watch?v=UoqDR0Hd9f0&t=3645s
I don't think anyone has seriously claimed that Modern Standard Arabic has been intentionally made complicated. It's clearly related to a lot of other Semitic languages (including the regional varieties of spoken Arabic). And the Category V thing is only about learning Arabic (any variety, not just MSA) as a second language, an in particular a second language for native speakers of English.